3G/4G mobile phones generally have a high current consumption (power consumption) resulting in short battery usage time with respect to other phones. Improving the current consumption and radio frequency (RF) performance would do much to improve the experience of users.
The front end circuit of a 3G/4G mobile phone includes at least a transceiver, a power amplifier (PA), a filter and an antenna. At present, there are three common solutions for reducing current consumption: averaging power tracking method, envelope tracking method and optimized load method. The averaging power tracking method reduces a supply voltage of the PA to increase PA efficiency. The advantages of this method are low cost and easy implementation, but the current consumption improvement is not significant when the power amplifier has a higher output power, and the averaging power tracking method cannot keep the RF performance at wireless condition. The envelope tracking method is used to track a transmitter signal envelope and provide a voltage which is related to signal envelope to the PA. The advantage of this method is better current consumption than the averaging power tracking method, but the disadvantages are higher cost, worse receiver (RX) band noise at PA output, and cannot keep the RF performance at wireless condition. The optimized load method is used to provide optimal impedance for PA output matching to obtain better efficiency and meet output power requirements. The advantage is low cost, but the disadvantages are limited current consumption and cannot keep the RF performance at wireless condition.
Regarding the above-mentioned optimized load method, the PA current consumption can ideally be optimized by tuning the PA output matching circuit based on 50 ohm loading. In a real case, however, the TX loading (impedance) is time-variant at wireless condition, and the current consumption and RF performance (e.g. the output power level or signal quality) of the PA may vary or be degraded when the user holds the phone in a different position. In addition, for different PAs, different transmitter (TX) frequencies and different PA output powers, the PA loading with best current consumption and RF performance will vary from 50 ohms.